1. Field of the Invention
The present invention relates to a cavity surrounded by a turbine casing for a gas turbine and a moving blade with a tip shroud.
2. Description of the Related Art
FIG. 3 is a cross sectional view which schematically shows a conventional gas turbine. In the drawing, reference numeral 1 denotes a main flow gas flowing from a combustor (not shown), reference numeral 2 denotes a casing for a turbine, reference numeral 3 denotes a disc, reference numeral 4 denotes a moving blade mounted to a periphery of the disc and arranged in several stages in an axial direction of the disc, and reference numeral 8 denotes a stationary blade disposed in the axial direction in an alternate manner with the moving blade 4.
In the gas turbine having the above structure, the main flow gas 1 of a high temperature supplied from the combustor (not shown) flows between the moving blade 4 and the stationary blade 8 in the axial direction. The moving blade 4 mounted to the disc 3 is rotated at a high speed so as to drive a rotor,thereby rotating a generator (not shown) connected to the rotor, so that power generation is performed.
FIG. 2 is a cross sectional view which shows a cavity of a tip shroud blade in a conventional gas turbine. In the drawing, reference numerals 3 to 4 denote the elements explained in FIG. 1 mentioned above, reference numeral 5 denotes a cavity, reference numeral 6 denotes a tip shroud for the moving blade 4, and reference numeral 7 denotes a fin disposed on the tip shroud. As shown in the drawing, the cavity 5 is constituted by a portion surrounded by the turbine casing 2, the tip shroud 6 and the fin 7. The volume of this cavity 5 is set to be large enough so as to prevent the rotating portion and the stationary portion from being in contact with each other due to a displacement caused by difference in a thermal expansion. As a result, the main flow gas 1 of a high temperature is entrained into the cavity 5, as shown by an arrow 1a, and a very large swirl 1b is produced.
As mentioned above, in the tip shroud blade cavity for the conventional gas turbine, since the cavity 5 is large, the main flow gas 1 of a high temperature is entrained and a very large swirl 1b is produced within the cavity 5, so that a large pressure loss is produced.
The pressure loss due to the production of the swirl 1b causes the lowering of a performance of the gas turbine.